The present invention relates generally to injection-molded articles made of thermoplastic resin (or molten resin), methods for manufacturing the molded article using injection molding, and injection molds and injection molding machines, and more particularly to a surface modification of a molded article using injection molding.
A wide variety of plastic molded articles are made using injection molding, and the plasticized molten resin materials determine their physical properties. The plastic molded article may be subject to various types of printing, coating, formations of electric conductors and metal films, junctions with another molded article, and other posttreatments. These necessary posttreatments generally activate a surface of the plastic molded article for surface modification and processing improvement.
On the other hand, the electroless plating is widely used to form a metal conductor film on a surface of an electronic apparatus made of the plastic molded article. The electronic plating procedure to plastic is generally pursuant to a flowchart shown in FIG. 15 although it slightly differs according to materials and other conditions.
The “degreasing” step initially removes the oil etc. from the surface of the molded article, and the “etching” step roughs the surface. The etching uses chrome acid solution and alkali metal hydroxide solution. The etchant requires a posttreatment, such as neutralization, causing increased cost, and the toxic etchant is problematic in handling. The “wetting” step then improves wettability using a process with surfactant solution, and the “catalyst (catalyzing)” step attaches catalyst to the plastic surface. For palladium catalyst, the “catalyzing” process impregnates the plastic in hydrochloric acid solution consisting of stannous chloride and palladium chloride. After the “catalyzing” step, the “accelerator (catalyst activation)” step activates plating catalyst using acid, such as sulfuric acid and hydrochloric acid. The “electroless plating” is not available until these processes finish.
Some processes have conventionally been proposed which rough a surface without etching (see for example, Japanese Laid-Open Patent Applications Nos. 9-59778 and 2001-303255). These references propose to form a thin film including plating catalyst on a plastic surface using organic binder and UV cure resin. Similarly, as disclosed, for example, in Japanese Laid-Open Patent Application No. 6-87964, technology has already known which irradiates ultraviolet (“UV”) laser onto and modifies a plastic surface in an atmosphere of gas, such as amine compounds. Other known surface modification technologies include corona discharge treatments, plasma treatments and UV treatments.
A semi-additive method has been known as one of methods that form wiring on a circuit board using electroless plating and electrolysis plating. FIG. 16 shows this flow. This method uses the “electroless plating” step to form a plated layer with a thickness of 1 to 2 μm on the entire substrate using the same steps as discussed above. Then, the “exposure and development” step follows with masking after a “photosensitive film and resist” are formed, so as to form film and resist layers that include a wiring pattern. The “electrolysis plating” step forms an electrolysis plated layer on the electroless plated layer that has exposed. After the film and resist are removed, soft etching forms plated wires by removing the electroless plated layer from part other than the wiring part. Due to bad adhesion properties with resin, the copper plating would sometimes require a posttreatment referred to as “black treatment”, which creates fine projections made of copper (oxide) to enhance an anchor effect with the resin.
Methods have also been conventionally proposed which provide a molded article with a three-dimensional circuit (see, for example, Japanese Laid-Open Patent Applications Nos. 4-76985 and 1-206692). These methods initially form a plastic three-dimensional circuit board by molding resin. Then, an electroless plated layer is entirely formed and the photoresist is entirely applied after the surface is roughed and catalyzed. The surface is exposed through a photomask and developed to remove part other than circuit-pattern forming part. The electrolysis plating and electroless plating using Ni and Au follow, and photoresist is peeled off and unnecessary portion of the electroless plating is removed. It is difficult to form the photoresist as a uniform three-dimensional structure. Japanese Laid-Open Patent Application No. 4-76985 proposes to use electrodeposition resist, but this resist has disadvantageously low alkali resistance.
A circuit forming method using injection molding has also proposed (see, for example, Japanese Laid-Open Patent Application No. 6-196840). Japanese Laid-Open Patent Application No. 6-196840 initially roughs a surface of a mold with Ra of 1 to 5 μm as a circuit forming surface, attaches catalyst cores onto the entire surface before injection molding, and forms the circuit board using injection molding, transferring the catalyst cores onto the entire surfaces. The electroless plating strongly adheres to a roughed molded surface that has strong adhesion property with the catalyst cores, and the other non-roughed part has such weak adhesion property that the non-roughed part may be removed with catalyst cores in etching that removes the electroless plated layer other than a circuit after the electrolysis plating.
No technologies have yet been proposed which may provide a surface modification simultaneous with an injection molding process and have a wide variety of applications. In addition, the conventional plastic electroless plating processes are complex and expensive as well as being problematic in handling waste disposal of many hazardous materials. The conventional processes that dispense with etching for roughing treat finished molded articles in a separate step, and thus are unsuitable for mass production. The conventional method that forms plated wiring on the plastic molded articles disadvantageously requires complex steps before and after the electroless plating, needs many toxic organic solvents, and roughs the plastic surface. The method disclosed in Japanese Laid-Open Patent Application No. 6-196840 may modify a plastic surface at the time of injection molding, but does not disclose a concrete way of uniformly attaching catalyst cores to the surface of the mold, as well as requiring not only circuit part on the surface to be roughed on the mold but also the etching step to be conducted after molding.